I appreciate the context that you have shared. You can sell in multiple currencies with Shopify Payments to allow your customers to view the prices of the products in their local currency. You can choose to have prices converted automatically using the current market exchange rate, or converted manually using an exchange rate that you choose. With that being said, it is not possible to allow your customers to change the currency within the checkout as this would require a coding change to the checkout, which is only available on Shopify Plus stores.
If you would like to sell in multiple currencies using the Shopify Payments gateway, feel more than welcome to use our step-by-step guide to enable selling in multiple currencies.
Let me know if you have any additional questions, happy to help out.